Polymer electrolyte fuel cells using solid polymer electrolyte membranes having proton conductivity operate at a lower temperature compared with other fuel cells, such as solid oxide fuel cells and molten carbonate fuel cells. Therefore, the polymer electrolyte fuel cells are receiving increased attention as a driving power source for use in moving bodies such as vehicles and have already been put to practical use.
Gas diffusion electrodes used in such polymer electrolyte fuel cells include electrode catalyst layers containing catalyst-supporting carbon fine particles covered with ion exchange resin (a polymer electrolyte) identical to, or different from, a polymer electrolyte membrane. The gas diffusion electrodes further include gas diffusion layers that supply reactant gas to the catalyst layers and collects charges generated in the catalyst layers. A membrane electrode assembly is formed in a manner such that the gas diffusion electrodes are assembled by bringing the catalyst layers into contact with the polymer electrolyte membrane. Plural membrane electrode assemblies are stacked on top of each other via separators having gas passages, so as to compose a polymer electrolyte fuel cell.
For example, Patent Literature 1 discloses such a gas diffusion electrode for a polymer electrolyte fuel cell in which a water-repellent layer is formed on a substrate formed of carbon paper, and a water-holding layer is formed between the water-repellent layer and an electrode catalyst layer. Here, the water-repellent layer contains Teflon (registered trademark) and carbon black, and the water-holding layer contains carbon black, crystalline carbon fiber (VGCF), and an ionomer.